1. Field of the Invention
The present invention relates to an electric helm device for use in steering a boat, and particularly, to a helm device comprising a stop mechanism which can apply resistance to the turning of a steering wheel.
2. Description of the Related Art
Conventionally, as a steering apparatus of an outboard motor, there has been known a steering apparatus comprising a hydraulic pump and a hydraulic actuator. A hydraulic pump is provided in a steering wheel (helm). A hydraulic actuator is disposed in an outboard motor and is driven by the hydraulic pump. In this type of steering apparatus, the direction of the outboard motor is changed by hydraulic pressure produced by the hydraulic pump. Also, a mechanical steering apparatus is known. In the mechanical steering apparatus, rotary motion of a steering wheel is transmitted to an outboard motor via a push-pull cable. Either type of steering apparatus is operated manually (i.e., by the boat operator's power). Accordingly, conventional steering apparatuses leave room for improvement in that a relatively large control force is required depending on the boat handling conditions.
Hence, electric steering apparatuses as disclosed in U.S. Pat. No. 7,137,347 (Patent Document 1) and WO 2012/023313A1 (Patent Document 2) have been contrived. An electric steering apparatus comprises a helm device comprising a sensor for detecting an operating angle of a steering wheel, and an actuator unit which is driven by electrical signals output from the helm device. In the electric steering apparatus, since the movement of a steering wheel is detected by a sensor, force for turning the steering wheel is extremely small. However, since it can even be dangerous for the steering wheel to be excessively turned with small force, resistance is applied to turning of the steering wheel by providing a friction mechanism in a helm unit. The friction mechanism comprises a plurality of fixed disks, a plurality of rotatable disks, and an electromagnet. The fixed disks and the rotatable disks are overlapped on one another alternately. The disks are composed such that they are pressed against one another by the electromagnet. Tooth portions formed on an outer peripheral portion of each of the fixed disks engage with a fixed spline member. Tooth portions formed on an inner peripheral portion of each of the rotatable disks engage with a rotatable spline member which rotates together with a steering shaft.
In the electric helm device, the steering wheel is locked by maximizing electric power to be supplied to the electromagnet to prevent the steering wheel from being turned further when it is operated to the maximum to the starboard or the port side. However, in order to turn the steering wheel to the opposite side, the aforementioned locked state must be cancelled. Accordingly, play is provided in an engagement portion between each tooth portion of the disk and the spline member.
In the conventional friction mechanism, play is provided in an engagement portion between each tooth portion of a disk and a spline member. In this case, if positions of all disks in the rotational direction are aligned with one another, the disks can be reversed within the range of the play relative to the spline member. However, due to vibration, etc., which is transmitted to a helm device during operation of the boat, positions of the respective disks in the rotational direction with respect to the spline member may be shifted from one another. In that case, the disks cannot be rotated relative to the spline member by the play. In order to solve the above problem, one idea was to provide an alignment mechanism for aligning the positions of the disks in the rotational direction, as described in Patent Document 2. However, a friction mechanism comprising such an alignment mechanism poses a problem that the structure becomes more complicated, and the number of components is increased.